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Sputtered Bismuth thin films as trace metal electrochemical sensors J. Baron1, P. Silva-Bermudez1 and S.E. Rodil1 1 Instituto de Investigaciones en Materiales, UNAM. Circuito Exterior s/n, C.U., C.P. 04510, Mexico D.F., Mexico.

ABSTRACT This work studies the performance of sputtered bismuth films as disposable working electrodes for stripping voltammetry. The electrodes were produced by coating a glass substrate with a bismuth film using DC magnetron sputtering under different conditions of power and time. The Bi-based sensors were characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. Electrochemical evaluation included linear sweep voltammetry using different buffer solution and pHs to observe the effect of the deposition conditions and thickness on the potential window accessible for stripping analysis. Subsequently, the electrodes were tested for the detection of low concentrations of trace metals (Cd(II) and Pb(II)) by square wave anodic stripping voltammetry (SWASV). Clear and reproducible stripping peaks were observed for trace concentrations in the 50 - 450 ppb range of the target analytes. The detection limit of the Bi electrodes were quantitatively estimated from the analyses of SWASV, demonstrating that even using simple sensor geometry, detection limits in the 14-20 ppb range could be obtained. The reproducibility of the measurements is good (relative standard deviations about 4%) after 10 consecutive measurements which define the maximum number of times that the sensor can be used. INTRODUCTION Electrochemical stripping analysis techniques have evolved as excellent methods for insitu detection of metal ions at very low concentration levels; µg per L (ppb) and even ng per L (ppt) detection limits have been reported [1]. Basically, heavy metal ions in a solution can be identified and quantified by sweeping a potential until reaching the specific potential at which the metal ions are reduced. Then the current generated at each reduction potential allows the identification of the metal ion species and their concentration (using calibration curves) within minutes. A major advantage of these techniques is that they are susceptible to be used for on-site environmental monitoring with relatively inexpensive and portable instrumentation. Hence, there is a growing interest on the development of disposable environmental sensors. The standard electrodes have been the Hg-film and the hanging Hg-drop electrodes due to the ability of Hg to form amalgams with many heavy metal ions. During the last decade, extensive research has been done looking for substitutes for the Hg-based electrodes due to the toxicity and difficulty on handling Hg and/or Hg salts [2-7]. In the search for alternative materials, different materials have been proposed including Pt, Au [8], diamond [9], Ir, etc. [10, 11], but none of them have reached the quality stripping performance of the Hg electrodes [12], or they are too expensive for disposable use. The main requirement for